During joint replacement surgery such as total hip arthroplasty, emboli in the form of marrow fat, medullary bony debris and cement are released into the patient's bloodstream. These emboli may be released into the inferior vena cava (IVC) in large quantities during the relocation of the prosthetic femoral head into the acetabular component, which sends a shower of embolic debris into the cardiopulmonary circulation. The emboli have detrimental effects due to both mechanical pulmonary arterial blockage and potentially cardiosuppressive activity, thus requiring the emboli to be filtered.
Conventional blood filtering devices are designed primarily to filter relatively large blood clots and to be permanently placed within the blood vessel. The majority of these filters include an anchoring device to prevent migration of the filter after placement. Once the filtering device is positioned within the blood vessel, the device is permanent.
An example of such a blood clot filtering device is disclosed in U.S. Pat. No. 4,619,246 issued Oct. 28, 1986 to Molgaard-Nielsen et al. This reference discloses a collapsible filter receptacle adapted to be introduced into a blood vessel for the purpose of entrapping thrombi and emboli in the patient's blood. The Molgaard-Nielsen device has a plurality of anchoring legs secured to the filter receptacle. The free end of each anchoring leg is bent outwardly to form a hook. When the filter receptacle is positioned within the blood vessel, each hook penetrates into the wall of the vessel to hold the filter receptacle in position, thus damaging the vessel wall. Similar examples are shown in U.S. Pat. No. 5,242,462 issued Sep. 7, 1993 to E1-Nounou et al. and more recently U.S. Pat. No. 5,324,304 issued Jun. 28, 1994 to Rasmussen.
There are several disadvantages to a permanently placed filter. First, some types, if not correctly seated in the IVC, have a markedly decreased filtering ability, thus necessitating placement of a second filter. Second, the filter may accumulate so much clot as to occlude the entire vena cava, a circumstance which occurs in up to 19% of cases. Third, the rate of rupture of the IVC may be as high as 15% due to erosion of the vessel wall by the anchoring hooks of the filter. Fourth, if removal becomes necessary, it almost always must be done surgically; moreover, removal may greatly damage the vessel because over time the filter's struts become endothelialized by the interior wall of the vena cava. Fifth, a patient with a permanent filter must take anticoagulant medication for life. These disadvantages are regrettable since the placement of the filter in the vein is usually only necessary for a limited time, corresponding to the period during which there is a real risk of embolism.
A technique has been developed for temporarily placing a removable vena caval filter so that it can be withdrawn at a later time. For this, a catheter remains inserted in the vein after the filter is deployed and projects from the body at the introduction site. Unlike the prior art, this filter is capable of being flushed while positioned within the blood vessel. Because the catheter projects from the skin, it constitutes a potential source of infection.
Another technique is disclosed in U.S. Pat. No. 5,300,086 issued Apr. 5, 1994 to Gory et al. In the Gory reference, the catheter is cut outside the jugular vein, crimped to seal the proximal end and sutured just below the surface of the skin. This technique significantly reduces the risk of infection. Unfortunately, the catheter, which is relatively rigid is uncomfortable for the patient. Moreover, as with the prior art, the filter is incapable of being flushed while positioned within the blood vessel.
Another technique is disclosed in U.S. Pat. No. 5,102,415 issued Apr. 7, 1992 to Guenther et al. This reference discloses a triple catheter having a receptacle at the distal end of an intermediate catheter and a suction device at the proximal end for assisting in the removal of debris during placement of the receptacle within the blood vessel. However, the receptacle is covered with an elastic coating or membrane and thus is incapable of filtering blood in the conventional sense. Thus, the receptacle is not a filter for emboli but only a receptacle for relatively large blood clots. Furthermore, the Guenther reference requires the use of an inflatable balloon attached to the distal end of the inner catheter, which forces the clot into the receptacle. The intermediate and inner catheters must then be completely removed from the outer catheter to remove the blood clot. The receptacle of the Guenther reference does not filter the blood and must be completely removed from the patient's body to remove the blood clot.